vii THE COLOURS OF THE LEPIDOPTERA 141 



relations existing between larvae and their environ- 

 ment. Mr. Poulton divides the colours of larvae into 

 two classes: (i) colours due to pigments derived 

 from the food, and (2) colours due to pigments 

 formed by the larvae. Of the chemical nature of the 

 pigments belonging to the second group we un- 

 fortunately know nothing ; they appear to be usually 

 though not invariably dark in colour, and are de- 

 posited in the cuticle or in the epidermis. Their 

 stability and their insolubility in alcohol suggest the 

 possibility that they may belong to the same group 

 as the dark pigments found in the adult. 



The pigments belonging to the first group are 

 green, yellow, or brown and are described by Mr. 

 Poulton as " modified chlorophyll " and xanthophyll. 

 Xanthophyll, as we have already explained, is the 

 lipochrome pigment which can be obtained from the 

 solutions of chlorophyll formed by steeping green 

 leaves in alcohol. The chlorophyll was recognised 

 in the larvae solely by certain resemblances between 

 the spectroscopic characters of the larval pigment 

 and those of green leaves. These pigments occur 

 primarily in the digestive tract, whence they seem to 

 reach the blood ; while from the blood they may be 

 deposited in the subcutaneous connective tissues. In 

 most cases it is only when they occur in the last 

 position that they are important in producing 

 coloration. In his first paper (1885) Mr. Poulton 

 supported his position that these pigments were 

 derived from the food by a number of arguments, 

 as well as by the results of spectroscopic examina- 

 tion. More recently (1893) he has been able to 

 demonstrate experimentally that the pigments are 



